Surface scanner for measuring the coordinates of points on a three-dimensional surface



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ii/nf ffnwfay United States Patent OF 3,53I,S63 SURFACE SCANNER FOR MEASURING THE C0- ()RDINATES 0F POINTS 0N A THREE-DIMEN- SIUNAL SURFACE Earle H. Stevenson, Detroit, Mich., assigner to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Filed Apr. 18, 1968, Ser. No. 722,472 Int. Cl. Glb 7/28 U.S. Cl. 33-174 11 Claims ABSTRACT 0F THE DISCLOSURE A multiple axis probe for measuring the coordinates of selected points on three-dimensional contours with reference to three principal reference axes wherein the probe may be adjusted with respect to any one reference axis or any combination of more than one reference axis up to ve in number.

GENERAL DESCRIPTION OF THE INVENTION My invention relates generally to a three-dimensional surface scanner system, and more particularly to a surface scanner having a surface contacting probe adapted for adjustment with respect to each of multiple reference axes as the coordinates of characteristic points on the surface are measured.

The improved surface scanner of my invention can be used in preparing three-dimensional templates and in preparations for machining three-dimensional die surfaces with arbitrary surface contours.

In machining geometric and arbitrary surface contours on dies and model surfaces, a multiple axis machine tool is used. The motion of the cutting tool is controlled by a numerical control system which receives its intelligence from a programmed tape, such as a magnetic tape or a punched paper tape. The intelligence on the tape is obtained by obtaining coordinate data along characteristic lines on a three-dimensional model of a surface corresponding to the surface to be machined. The point coordinates in three dimensions then are plotted on a two-dimensional draft plate. The data in two dimensions are scanned by a coordinatograph, which registers the coordinates of selected points by means of computer-assisted data processing steps. The two dimensional draft plate data are transferred to a numerical control tape which in turn is used as the input element for the numerical control system of the machine tool.

The improvement of my invention resides principally in the surface scanner which obtains point coordinates in the early steps of the data processing method.

In many three-dimensional surfaces for the models used in environments of this type, the contours in various surface Zones vary sharply from one attitude to another. That is, the normal vectors at closely adjacent points on the surface will be at widely varying angles when a characteristic line containing such points is drawn through the surface zones. It becomes difficult to maneuver a surface scanning probe along the characteristic line when conventional surface scanner systems are used. My improved surface scanner system overcomes this difficulty, however, by providing a scanner probing head that is capable of adjustment about two additional axes in addition to the axes that are parallel to the three principal coordinate axes to which the coordinates of the measured points on the characteristic line are referred.

As the scanning probe on the surface scanner is directed along the characteristic lines on a three-dimensional surface of a model, the changes in the position of the contact point of the probe with respect to each of 3,531,868 Patented Oct. 6, 1970 ice the three coordinate axes are measured by separate digitizers identied as the Y-axis digitizer, the Z-axis digitizer and the X-axis digitizer. The probe can be adjusted through a plurality of positions to suit any particular surface configurations without changing the location of the probe surface contacting tip with reference to the three coordinate axes. Provision is made for automatically varying the position of the probe in directions parallel to the three principal coordinate axes. The adjustment of the probe with respect to either of its other two axes will not change the position of the surface contacting tip of the probe with respect to the remaining three coordinate axes.

The means for adjusting the probe in the direction of one axis comprises in part a closed servoloop circuit. This circuit permits the probe to be advanced in the direction of a coordinate axis until contact is made between the probe tip and the surface to be measured. At that time the closed circuit will interrupt the motion of the probe in the direction of that axis and an appropriate reading of the coordinates for the point that is contacted then is recorded. At the same time the other two principal coordinates of that same point are recorded by separate readout units associated respectively with each of the other axes.

The surface-engaging probe element can be adjusted in the direction of one of three principal coordinate axes of the scanner and two additional probe adjustments can be obtained during the scanning operation, one of the adjustments being about an axis parallel to one of the coordinate axes and the other adjustment being about an axis that forms an angle with respect to each of the coordinate axes.

Automatic means is provided for adjustment of the probe in the direction of each of the three coordinate axes, at least one of the adjusting means forming a part of the aforesaid closed servoloop circuit which senses engagement of the probe tip with the measured surface. 'Ihe scanner system will respond to a predetermined pressure exerted by the probe on the measured surface either to effect an adjustment of the probe toward the surface when the contacting force is less than a predetermined value or to withdraw the probe away from the surface when the contacting force is greater than that predetermined value.

BRIEF DESCRIPTION OF THE INVENTION FIGS. 1A and 1B show in isometric form a surface scanner situated for measuring surface data on a threedimensional clay model of an automotive vehicle.

FIG. 2 is a side elevation view, partly in section, of a portion of the. structure of FIG. l.

FIGS. 3A and 3B show a plan view of the structure in FIG. 2.

FIG. 4 shows an alternate construction for mounting the scanner assembly.

FIG. 5 shows another alternate construction for mounting the scanner assembly.

FIG. 6 shows still another alternate construction for mounting the scanner assembly.

FIGS. 7A, 7B, 7C, 7D and 7E show in enlarged form theprobe head of the scanner system of my invention in varlous operating positions.

FIG. 7F is a sectional View taken along section line 7F-7F of FIG. 7D.

FIG. 7G is a sectional view taken along section line 7G-7G of FIG. 7D.

FIGS. 8A to 8D show in schematic form the direction of movement of the scanning head of the three-dimensional clay model along characteristic lines.

FIG. 9 shows the surface probe head used with the structure of FIG, 7. 

